Oscillators are widely used in electronic circuits for generating a clock signal. Those clock signals are, for example, used in switching converters for defining the frequency of a pulsewidth modulated (PWM) signal, in digital circuits for synchronizing the operation of individual devices in the digital circuit, or in communication devices for synchronizing a transmitter and a receiver each coupled to a transmission channel.
Different types of oscillators are known, such as quartz oscillators, micromechanical oscillators, or relaxation oscillators. Relaxation oscillators include a capacitive component that is periodically charged and discharged with a constant current in order to generate a triangular oscillating signal. In this kind of oscillator, a voltage across the capacitive component is compared with at least one reference voltage in order to define the times when the oscillator switches between charging and discharging, and vice versa, of the capacitive component. This requires the use of at least one comparator. Comparators, however, have a propagation delay that is dependent on a plurality of different factors and that influence the frequency of the oscillating signal. The propagation delay of a comparator can be dependent on variations in its manufacturing process, but also on external factors during its operation, such as the ambient temperature. Those external factors, that may vary over time, may result in an oscillating signal with a time-varying frequency.
There is a need to provide a relaxation oscillator that generates an oscillating signal with a stable frequency and that can be integrated in an integrated circuit, and to provide a method for generating an oscillating signal with a fixed frequency.